LEARN ABOUT

SOLAR SYSTEM

The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest eight are the planets, with the remainder being smaller objects, such as dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury.

The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.

The Solar System also contains smaller objects. The asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, and beyond them a newly discovered population of sednoids. Within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets. Identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to these two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between regions. Six of the planets, at least four of the dwarf planets, and many of the smaller bodies are orbited by natural satellites, usually termed "moons" after the Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects.

+ PLANETS IN THE SOLAR SYSTEM

+ THE HOTTEST PLANET IN THE SOLAR SYSTEM

Venus is the second planet from the sun and has a temperature that is maintained at 462 degrees Celsius, no matter where you go on the planet. It is the hottest planet in the solar system. So what makes Venus hotter than Mercury? Mercury doesn't have any atmosphere, and atmosphere can hold and trap heat.

+ HOW MANY SUNS ARE THERE IN THE SOLAR SYSTEM?

For many years scientists have studied our own solar system. But until the last few years, we knew of no other solar systems. This may seem surprising, as the Sun is one of about 200 billion stars (or perhaps more) just in the Milky Way galaxy alone.

+ WHAT MAKES UP OUR SOLAR SYSTEM?

The solar system is made up of the Sun, the 8 planets and 5 dwarf planets and their 181 known moons, asteroids, comets, dust and gas. The planets, asteroids, and comets travel around the Sun, the center of our solar system.

+ WHAT IS THE CLOSEST SOLAR SYSTEM TO OURS?

The two main stars are Alpha Centauri A and Alpha Centauri B, which form a binary pair. They are an average of 4.3 light-years from Earth. The third star is Proxima Centauri. It is about 4.22 light-years from Earth and is the closest star other than the sun.

+ WHAT IS THE KUIPER BELT?

The Kuiper Belt is a comet-rich area of our solar system that begins near the orbit of Neptune and continues beyond Pluto. The belt's inner edge is about 30 astronomical units (AU) away from the Sun. Its outer edge is about 50 AU away from the Sun.

The Kuiper Belt, an area in space beyond Neptune, characterized by asteroids, ice and rock is also home to several dwarf planets. Haumea, Makemake, and our dearly demoted Pluto all reside in the Kuiper Belt. Outside the Kuiper Belt, there are only two other known dwarf planets Ceres and Eris.

+ WHAT’S AN AU?

An Astronomical Unit (AU) is the average distance between Earth and the Sun, which is about 93 million miles or 150 million kilometres. Astronomical units are usually used to measure distances within our Solar System.

+ WHATS THE OORT CLOUD

The Oort Cloud is an extended shell of icy objects that exist in the outermost reaches of the solar system. It is named after astronomer Jan Oort, who first theorised its existence. The Oort Cloud is roughly spherical, and is thought to be the origin of most of the long-period comets that have been observed. They do not stay on the same flat plane. These objects break the rules of the Solar System and create a sphere of comets around the Sun. It is believed that the Oort cloud formed as trillions of comets where thrown out of the inner Solar System by Jupiter and Saturn. The Oort cloud has never been observed but is thought to be a spherical distribution of icy objects like comets orbiting our Sun at distances between 3000 and 100,000AU. It is also believed to be the origin of many of the long-period comets in the solar system.

+ THE ASTEROID BELT

The Asteroid Belt is located in an area of space between the orbits of Mars and Jupiter. That places it between 2.2 and 3.2 astronomical units (AU) from the Sun. The belt is about 1 AU thick. The average distance between objects in the Asteroid Belt is quite large. Scattered in orbits around the sun are bits and pieces of rock left over from the dawn of the solar system. Most of these objects, called planetoids or asteroids — meaning "star-like" — orbit between Mars and Jupiter in a grouping known as the Main Asteroid Belt.

The asteroid belt formed from the primordial solar nebula as a group of planetesimals. Planetesimals are the smaller precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much orbital energy for them to accrete into a planet.
Ceres is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter, slightly closer to Mars' orbit. Its diameter is approximately 945 kilometres (587 miles), making it the largest of the minor planets within the orbit of Neptune.